Throttle upstream pressure estimating apparatus and cylinder charged air quantity calculating apparatus for internal combustion engine

Abstract

In a non-critical pressure region where a pressure ratio [Pm/Pthrup(i−1)] of an intake air pressure Pm (throttle downstream pressure) detected by an intake air pressure sensor to a previous throttle upstream pressure Pthrup(i−1) is greater than a predetermined value B, the previous throttle upstream pressure Pthrup(i−1) is substituted for one of two terms of the throttle upstream pressures Pthrup(i) included in an intake system model so that present throttle upstream pressure Pthrup(i) is calculated. In a critical pressure region where the pressure ratio is less than or equal to the predetermined value B, a physical value f(Pm/Pthrup(i)) using a pressure ratio [Pm/Pthrup(i)] of the intake air pressure Pm to a present throttle upstream pressure Pthrup(i) as a parameter is regarded as a steady value fc so that the present throttle upstream pressure Pthrup(i) is calculated.

1. A cylinder charged air quantity calculating apparatus for an internal combustion engine which calculates a cylinder charged air quantity by using an equation of an intake system model including a throttle flow rate parameter which represents a flow rate parameter depending on a throttle opening degree, the cylinder charged air quantity calculating apparatus comprising:
 storage means for staring a map defining a relationship between a throttle opening degree and a throttle flow rate parameter; 
 learning means for determining whether a predetermined learning execution condition is fulfilled and for learning, when the predetermined learning execution condition is fulfilled, a learning correction amount with respect to a map value based on a deviation between an actual value of the throttle flow rate parameter calculated according to a present throttle opening degree by using the equation of the intake system model and the map value of the throttle flow rate parameter read from the storage means; 
 correcting means for correcting the map value of the throttle flow rate parameter corresponding to a present throttle opening degree read from the storage means during an operating state of the internal combustion engine by using the learning correction amount; and 
 cylinder charged air quantity calculating means for calculating a cylinder charged air quantity by using the map value of the throttle flow rate parameter corrected by the correcting means during an operation of the internal combustion engine, wherein 
 the internal combustion engine is provided with a supercharger; and 
 the predetermined learning execution condition is at least: 
 (1) the engine is in a steady operation state in which a change in an intake air quantity is small; 
 (2) the engine is in a low air quantity region in which the intake air quantity is less than or equal to a predetermined value; and 
 (3) a pressure ratio Pm/Pthrup of the throttle downstream pressure Pm to the throttle valve upstream pressure Pthrup is less than or equal to a predetermined value. 
 
     
     
       2. A cylinder charged air quantity calculating apparatus for an internal combustion engine according to  claim 1 , further comprising:
 throttle upstream pressure estimating means for estimating throttle upstream pressure by using the equation of the intake system model during an operation of the internal combustion engine; 
 wherein the throttle upstream pressure estimating means estimates a throttle upstream pressure by substituting the map value of the throttle flow rate parameter corrected by the correcting means into the equation of the intake system model.